Method for packet data transmission

ABSTRACT

A method for packet data transmission in a communication system is disclosed, where the packet data includes a first type of data packet and at least one alternative second type of data packet. According to the method, quality modifications of a transmission channel used as a connection between a data source and data sinks are detected and, according to the detected quality modification, a data packet type of a successive data packet to be transmitted via the transmission channel is selected.

The invention relates to a method for packet data transmission

BACKGROUND

Generally, in information and telecommunications technology thesegmenting and successive transmission payload data to be transmitted isknown. Furthermore it is generally known that as payload data or payloadinformation control information is appended to these data segments,generally referred to as data packet, for example addressing data,transmission sequence, flow control and error correction, so that thedata packets can be assigned to the correct recipient and so that aftertransmission is completed, any necessary error handling can be performedon the receive side and the data packets—data segments—can bereassembled correctly again.

When a data packet of this type passes through a number of layers whichin their turn are assigned protocols, especially error protocols, beforebeing transmitted over a physical channel—for which provision is made inaccordance with the OSI reference model for example—, the payload dataof a data packet will mostly be encapsulated within a number of items ofcontrol information assigned to the individual layers or protocols, withdata for error correction in each case.

The control information appended to the payload data in this way resultsin it occupying the capacity of the transmission channel/channels andthus reducing the payload data rate or the payload data throughput.

SUMMARY

Under the present disclosure, the throughput of payload data may beincreased.

Under the method for packet data transmission in accordance with thepresent disclosure, with a first data packet type and at least onealternate second data packet type, changes in quality of a transmissionchannel used for a connection between a data source and a data sink FromEP 1 089 502 A2 a radio communications system as well as a method isknown in which parameters for the transmission of audio and video dataare selected depending on the characteristics of a wireless connectionfor said transmission.

From EP 1 109 343 A2 an adaptive method for operating a channel coder isknown which, on the basis of characteristics of a current wirelessconnection, controls the channel coder in such a way that it switchesbetween different forms of channel coding.

From U.S. Pat. No. 6,262,924 B1 an arrangement for optimizing abidirectional radio data transmission is known in which a transmissiondevice can select different types of modulation.

However, using the disclosed methods, the throughput of payload data maybe increased over the prior art.

With the method for packet data transmission in accordance with theinvention, with a first data packet type and at least one alternatesecond data packet type, changes in quality of a transmission channelused for a connection between a data source and a data sink are recordedand, depending on the change in quality recorded, a packet type of afollowing data packet to be transmitted over the channel will beselected.

The inventive method can be advantageously implemented in a radiocommunications system.

Selecting a second data packet type which features a lower proportion ofcontrol data than the first data packet type in the case where thetransmission channel is of good quality results in more effective use ofthe transmission channel.

A development of this is to select a data packet type which features asmaller number of error coding bits. The advantage of this developmentis that the redundant data provided for error coding can be saved, sothat the control data part of a packet can be reduced without leavingout information.

A simple implementation is achieved if a good quality is signaled onreaching a first threshold value by a variable reflecting the quality ofthe transmission channel small.

The advantage of recording the change in quality on the data sink sideis that changes in quality that cannot be recorded by the data sourcecan be detected by the data sink, in particular an error rate determinedthere, and transmitted to the data source, so as to largely ensure thatit is possible to react to all faults on the transmission channel.

Under an exemplary embodiment, to determine the change in quality, anumber of packet retries are recorded and/or a field strengthmeasurement of received signals is taken reflecting the quality of thetransmission channel.

Implementing the method in a radio telecommunications system whichfunctions in accordance with the Bluetooth Standard has the advantage ofsimple implementation, since according to the Bluetooth Standarddifferent data packet types, for example DM5, DH5 or AUX1, are provided,which differ especially in the number of bits provided for an errorcorrection.

Advantageous combinations of data packets are produced when

a) the first data packet type is embodied as per Bluetooth as a DM5packet,

b) the second data packet type is embodied as per Bluetooth as a DH5packet.

or

a) the first data packet type is embodied as per Bluetooth as a DM5packet,

b) the second data packet type is embodied as per Bluetooth as an AUX1packet,in which case any given further combination of data packet typessuggested for Bluetooth is conceivable, provided they achieve thedesired effect—more effective use of the transmission channel toincrease the data rate.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure contained herein will be more readily understood byreference to the following detailed description taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 illustrates an exemplary flowchart of an adaptive data packettype selection in a radio telecommunications system functioning inaccordance with the Bluetooth short-range standard for optimizing thedata throughput when there are qualitative changes to the transmissionchannel.

DETAILED DESCRIPTION

Turning to FIG. 1, in a first step S1 the exemplary method is in itsinitial state. In this state the procedure is running, under the controlof a microprocessor of a terminal carrying a Bluetooth radio module forexample, especially as an interrupt-controlled background process.

An interrupt would be a file transmission requested by the terminal forexample. If this occurs, a first packet, generally the first of a numberof packets, is sent in a second step S2.

For this the data packet is initially constructed in accordance with afirst present data packet type, which with Bluetooth systems willgenerally be a DM5 packet.

The DM5 packet features a payload data area of 226 bytes, in which casethis area also contains error coding (Forward Error Correction, FEC)with an additional 16-bit CRC for the payload data area, so that thetransmission of this type of packet uses up to five time slots.

Subsequently, in a third step S3, the channel quality of a channel usedfor this packet data transmission is recorded.

The number of packet retries, which can be evaluated by the senderitself, can serve as a measure for determining the channel quality here.

This measure can however be combined with other metrics or even replacedby other metrics which can be included for estimating channel quality,in which case metrics can also be used which allow evaluation on thereceiver side

For example this can be done in such a way that a receiver—a furtherterminal equipped with a Bluetooth radio module—of the data packetevaluates the error rate of the received data packet (CyclicalRedundancy Check, CRC error) or the receive field strength of a signaltransferring the data packet (Received Signal Strength Indication,RSSI), so that in a fourth step S4 a check can be made on whether thedata packet type currently being used is required.

The check carried out in the fourth step S4 is undertaken in such a waythat when the channel quality reaches a first threshold value, forexample when the number of packet retries has dropped below a particularvalue, which could also be signaled to the sender—after introduction ofthe corresponding signaling process in the standard—by the receiver, thedecision is taken in the sender to select a suitable data packet type.

For a system functioning in accordance with the Bluetooth Standard thiswill generally involve the DH5 packet type.

The DH5 packet has a similar structure to the DM5 packet but differs inthat it features a payload data area of 341 bytes in length, with themajor difference being that with DH no error coding is contained in thepayload data area, but exactly like the DM5 there is an additional16-bit CRC and transmission is also in up to five time slots.

By Checking whether a currently used packet type matches the currentcharacteristics of the transmission channel it is possible to ensure atif there is a change to the quality of the transmission channel amaximum possible net or user data rate is guaranteed.

When the quality of the transmission channel drops again, which isnoticeable by a falling of the net or user data rate, since the numberof bit errors increases the first data packet type is selected the nexttime that step S4 is executed.

An extension or alternative to the third step S3 and the fourth step S4is produced by defining a first data packet type as the default, so thatto identify an improvement in the channel characteristics, the seconddata packet type is defined at regular intervals so that a higher net oruser data rate is produced

Alternatively in the fourth step S4 a second threshold value can also beused as the lower limit for the channel quality which is reached whenfor example the number of recorded packet retries exceeds a particularvalue, so that on reaching this second threshold value the first datapacket type is chosen.

On the basis of the exemplary embodiment for a telecommunications devicefunctioning in accordance with Bluetooth, this means that initially inthe fourth step S4 a switch is made from ⅔ FEC coded first data packettype DM5 to the uncoded second data packet type DH5. When in asubsequent run the quality of the transmission channel drops again, thenet or user data rate falls because the bit error rate increases.

This leads to an increase in number of packet retries which serve instep S4 as a measure for determining the quality of the transmissionchannel.

If the number of packet retries exceeds a specific defined value, thequality falls below the second threshold value so that the sender inthis case selects the more suitable first data packet type DM5

A switch back to the second data packet type DH5 can take place if thevalue drops below a lower limit for the number of packet retries onsending DM5 packets, i.e. if it reaches the first threshold value.

As an alternative to this there can be a switch at regular intervals totransmitting data packets in accordance with the second data packet typeand then after a further execution of the first step S1 and second stepS2, in a third step S3 to establish whether the channel characteristicshave improved by checking whether the number of package retries hasincreased, if it has not the second data packet type is retained in thefourth step S4, otherwise the first data packet type is selected again.

If a change of data packet type is determined in the fourth step S4, itmust be established in a fifth step whether the data source involved isthe master or the slave of a telecommunications network. This check isrequired in systems with a hierarchical structure in which asuperordinate communications device prespecifies technical parametersfor the connection. Such a hierarchical structure is especiallyspecified in systems functioning in accordance with Bluetooth by themaster-slave architecture in such systems.

If the interrogation in the fifth step reveals that this device is themaster, the switch-over to another data packet type can be undertakenimmediately in the following seventh step and the procedure can switchto the initial state in first step S1. If the device is the slave, thismust first send a request to the master in a sixth step S6 so that theseventh step S7 can be performed.

The execution sequence of the procedure described in accordance with theinvention should not just be restricted to Bluetooth systems that can beused for data applications for which a highest possible data rate, evenunder difficult conditions such as for example at the limit of coverageor with interference from other transmitters (e.g. microwave), isrequired.

While the invention has been described with reference to one or moreexemplary embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiments disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. A method for packet data transmission in a Bluetooth radiocommunication system, wherein the packet data comprises a first datapacket type and at least one different second data packet type,comprising the steps of: recording changes in a quality of atransmission channel used for a connection between a first data sourceand a data sink; depending on the changes in the quality recorded,switching back and forth between the first data packet type and the atleast one different second data packet type for subsequent data packetsto be sent over the transmission channel, wherein a) the first datapacket type is a DM5 packet, and b) the at least one different seconddata packet type is a DH5 packet, and wherein the step of switching backand forth between the first data packet type and the at least onedifferent second data packet type comprises determining if the firstdata source is a master data source or a slave data source, and if thefirst data source is the master, then the switch to another data packettype is made immediately, and if the first data source is the slave,then the switch to another data packet type is made after requesting toa master of the slave the data packet type switch.
 2. The methodaccording to claim 1, wherein based at least the recorded changes,transmitting the second data packet type, wherein the second data packettype features a lower proportion of control data than the first datapacket type.
 3. The method according to claim 2, wherein the second datapacket type features a lower number of error coding bits compared to thefirst data packet type.
 4. The method according to claim 2, wherein thegood quality is signaled upon reaching a first threshold value of avariable reflecting the quality of the transmission channel.
 5. Themethod according to claim 2, wherein, for a transmission channel with abad quality, the first data packet type is selected, the bad qualitybeing signaled when a second threshold value is reached.
 6. The methodaccording to claim 1, wherein the change in quality is recorded on thedata source side.
 7. The method according to claim 1, wherein a) thechange in quality is recorded on the data sink side, and b) a messagespecifying the change in quality is transmitted from a data sink to thedata source.
 8. The method according to claim 1, wherein, to determinethe change in quality, one of (a) a number of packet retries arerecorded, and (b) a field strength measurement of received signals istaken, reflecting the quality of the transmission channel.
 9. A methodfor packet data transmission in a Bluetooth radio communication system,wherein the packet data comprises a DM5 data packet type and at leastone DH5 data packet type, the method comprising the steps of: recordingchanges in a quality of a transmission channel used for a connectionbetween a first data source and a data sink, wherein the changes inquality are defined by a first threshold and a second threshold;selecting a subsequent data packet type to be a DM5 data packet type ifthe change in the quality reaches the first threshold; selecting asubsequent data packet type to be a DH5 data packet type if the changein the quality reaches the second threshold; and switching back andforth between the DM5 data packet type and the at least one DH5 datapacket type based on the changes in the quality of the transmissionchannel, wherein the step of switching back and forth between the DM5packet type and the at least one DH5 data packet type comprisesdetermining if the first data source is a master data source or a slavedata source, and if the first data source is the master, then the switchto another data packet type is made immediately, and if the first datasource is the slave, then the switch to another data packet type is madeafter requesting to a master of the slave the data packet type switch.10. The method according to claim 9, wherein the first thresholdindicates a better quality, compared to the second threshold.